A team of researchers from the University of Virginia (UVA) School of Medicine has made a landmark discovery of vessels that connect the brain with the lymphatic system – something that wasn't previously thought to exist. The breakthrough has significant implications on the study of major neurological diseases, from multiple sclerosis to Alzheimer's.

The link between the brain and the immune system has long been shrouded in mystery – up until now that is. The new research makes a direct connection between the two, showing that the brain is in fact connected to the immune system through lymphatic vessels, just like every other tissue in the body.

The discovery was made during the study of the meninges – the membranes that cover the brain – of a mouse. The researchers developed a new method to mount the meninges on a single slide, fixing it within the skullcap before dissection. This allowed them to examine it as a whole, which is when they noticed a pattern of vessels in the distribution of immune cells. Testing confirmed that they were lymphatic vessels.

The lymphatic vessels have eluded discovery up until now thanks to their close proximity to a major blood vessel that leads down into the sinuses. The area is difficult to image, making the vessels easy to miss.

"Instead of asking, 'How do we study the immune response of the brain?' 'Why do multiple sclerosis patients have the immune attacks?' now we can approach this mechanistically," says Prof. Jonathan Kipnis. "It changes entirely the way we perceive the neuro-immune interaction. We always perceived it before as something esoteric that can't be studied. But now we can ask mechanistic questions."

The confirmed presence of the lymphatic vessels will lead to significant reassessment of our understanding of the workings of the brain and diseases that affect it. For example, the researchers believe that the findings may have some big implications on the study of Alzheimer's, wherein chunks of protein accumulate in the brain. It's thought possible that this might be due to the lymphatic vessels not doing their job as they're supposed to.